1. Field of the Invention
The present invention relates to an image reproducing apparatus such as a copying machine.
2. Description of the Prior Art
A copying machine has been proposed recently to detect a density of an original image optically or electrically (based on potential levels) and to reproduce an image with an appropriate density (to be referred to as AE hereinafter).
In an apparatus of this type, an optical system is moved in the forward direction when prescanning for AE is performed. During this forward movement of the optical image, AE measurement is performed and the density of the image is read. The read density is held, and the moving direction of the optical system is inverted from the forward direction to the backward direction at a home position (to be referred to as home position B hereinafter) which is different from a home position (to be referred to as home position A hereinafter) in the steady state. The optical system then returns to the home position A. The amount of light emitted from the original exposure lamp is controlled in accordance with the detected original density obtained by the AE measurement and the desired image is formed.
However, in a copying machine with an ADF (Automatic Document Feeder), prescanning for the AE measurement cannot be performed while original sheets are being fed and discharged by the ADF.
Accordingly, sheet feed and discharge by the ADF or prescanning for AE cause a decrease in the copying speed.
In copying different sizes, the scanning speed or scanning stroke is changed. In such cases, when AE control is performed in accordance with the measured original density, the image quality becomes different from that expected.
When AE control is performed with high precision in accordance with the measured original density, the reproduced image frequently becomes too dark or too weak (bright).
When the original density is measured, the previous measurement must be reset (cleared). However, if such resetting is performed at the beginning of the copying operation, an erroneous signal is stored and the control precision is degraded. Furthermore, if this resetting is performed too frequently, it may even be performed during interruption of the copying operation, thus further lowering the copying speed.
Although it is desired to warn or display conditions associated with image reproduction, this also requires a great number of indicators and/or displays and degrades the outer appearance of the control console of the copying machine.
Accordingly, it is an object of the present invention to provide an image reproducing apparatus which is free from such conventional drawbacks.
It is another object of the present invention to provide an image reproducing apparatus which is free from time loss due to image density control.
It is still another object of the present invention to provide an image reproducing apparatus which is capable of optimal image density measurement.
It is still another object of the present invention to provide an image reproducing apparatus which is capable of reproducing a stable image of optimal density even if the copying mode is changed from the normal size to in a different size.
It is still another object of the present invention to provide an image reproducing apparatus in which the copying speed is not decreased even if an additional device such as an ADF is added.
It is still another object of the present invention to provide an image reproducing apparatus which is capable of providing nonoptimal warning displays such as image reproducing conditions with a fewer number of displays and/or indicators. The above and other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings.